Preparation Of Thermally Activated Copper Tailings-gangue And Alkali-excited Cementitious Materials

Alkali-stimulated cementitious material is a kind of new cementitious material which is different from Portland cement in raw material,formation mechanism,hydration products and production industry.It is formed by the dissolution,gel,reconstruction,polymerization and hardening of the silicate aluminate components in the raw material.The mineral composition is similar to that of zeolite,and the physical morphology is three-dimensional network structure,so it has better performance.In this paper,copper tailings and coal gangue were taken as the research objects,copper tailings based alkali activated cementitious materials were prepared through thermal activation and alkali activation,and the influence of various influencing factors on compressive strength was explored.The heavy metal leaching performance and microstructure of the gel cementitious materials were analyzed,and the resistance study was carried out,and the following conclusions were drawn:In the study of the basic characteristics of copper tailings and coal gangue,it is found that the average particle size of copper tailings is 112.47μm,the boundary particle size（D10,D90）=（12.62,282.51）,the degree of dispersion is small,the distribution is uniform,and the particle surface is relatively smooth.Its main mineral composition is dolomite（Ca Mg（CO₃）₂）,quartz（Si O₂）,belongs to the high silicon,high calcium and low aluminum materials,the main chemical composition is Si O₂,Ca O,Mg O and Al₂O₃.Coal gangue is a material with high silicon,high aluminum and low calcium,and its main chemical composition is Si O₂,Al₂O₃,Fe₂O₃ and Ti O₂.Its main mineral composition is kaolinite(Al₄[Si₄O₁₀]（OH）₈),both of which have relatively smooth surface.After thermal activation of copper tailings and coal gangue,the material composition and structure of copper tailings and coal gangue are changed by XRD,SEM,FTIR and alkali leaching.The dolomite and quartz in copper tailings and kaolinite in coal gangue decompose under high temperature.The content of active silicon and aluminum in copper tailings and coal gangue before and after thermal activation was measured by alkali leaching experiment.It was found that the activation effect of copper tailings was the best when the calcination temperature was 800℃,and the leaching concentration of silicon and aluminum was 38.42mg/kg and 7.32mg/kg,respectively,which increased by 79.70%and 64.49%compared with that before calcination.When the calcination temperature of coal gangue is 600℃,its activation effect is the best,and the leaching concentration of silicon and aluminum reaches301.6mg/kg and 342.3mg/kg,which are 6.2 times and 35 times higher than before calcination,respectively.Compared with sodium hydroxide and potassium hydroxide,liquid water glass is better for preparing copper tailings cementitious material.When the addition amount of water glass is 30%and the modulus is 1.6,the best compressive strength can reach 11MPa.Adding gangue can significantly improve the compressive strength of copper tailings cementitious material.When adding gangue with 30%calcination temperature of 600℃,the compressive strength can reach 18MPa.By analyzing the content of sodium silicate,the modulus of sodium silicate and the content of coal gangue through response surface,it is found that the influence of the several factors is:coal-gangue content>sodium silicate content>modulus of sodium silicate.The best theoretical conditions are as follows:sodium silicate content=39%,sodium silicate modulus=1.55;Coal gangue content=38%.In the actual operation room,the content of sodium silicate is 39%,the modulus of sodium silicate is 1.5,and the content of coal-gangue is 38%,and the compressive strength is 17.3MPa,the margin of error is 2%,within a reasonable range.Through methods such as XRD,SEM,FTIR the gelled material microstructure were characterized,found that most of the silicon aluminate phase through dissolving-refactoring-polymerization-after curing reaction to form gel material such as the internal structure of particles is no longer a uniform distribution of particles,but surface,with a range of caking of non-uniform granular gel product,FTIR chart also shows that polymer form relatively full.Through the toxicity analysis of heavy metals leaching from copper tailings and coal gangue raw materials,only the leaching concentration of Cu²⁺in the original copper tailings is 220mg/L,which is more than100mg/L of hazardous waste identification standard,and the leaching concentration of other heavy metals is within the standard range.At the same time,the influence of the content of sodium silicate,the modulus of sodium silicate and the content of coal gangue on the leaching concentration of Cu²⁺in cementified materials was compared.It was found that the addition of coal gangue had the best stabilizing effect on the leaching concentration of Cu²⁺in cementified materials,and the leaching concentration ranged from 2.2 to 4.8mg/L.It was found that the cementitious materials prepared under the optimal conditions were subjected to high temperature calcination,acid leaching and alkali leaching.When the calcination temperature reaches 200℃,the compressive strength of the cementitious material increases,but when the temperature is higher than 200℃,the compressive strength of the cementitious material decreases gradually.At the same time,the decomposition of moisture,ash and structure is accompanied in the whole process,which leads to the continuous loss of the quality of the cementitious material.After soaking in acidic conditions,the compressive strength of the cementitious material decreases with the increase of the concentration,and the mass loss rate also gradually increases,with an in inverse relationship between the two.When the concentration of H₂SO₄ solution is 1mol/L,the compressive strength of the cementitious material in 14d is 6.8MPa,and the mass loss rate is 13.8%.After soaking in alkaline conditions,the compressive strength of cementitious materials first increases and decreases with the increase of concentration,but the mass loss rate gradually increases at higher alkali concentration,which is different from that under acid leaching conditions.When the concentration of NaOH reaches 1mol/L,the 14d compressive strength of cementitious materials is 9.2MPa,and the mass loss rate is8.5%.Although the alkali resistance is better than the acid resistance,the corrosion resistance of copper tailings composite cementitious materials is poor in general.